Stabilizing method and device



J. NEUFELD STABILIZING METHOD AND DEVICE Filed Nov. 25, 1936 4 Sheets-Sheet 1 lllllllllllllll J a Ease. NE

I .mveufo g W Feb. 13, J. NEUFELD STABILIZING METHOD AND DEVICE Filed Nov. 25, 1936 4 sheets s eet 2 INVENTOR Feb. 13, 1940. J. NEUFELD 2,190,037

STABILIZING METHOD AND DEVICE Filed NOV. 25, 1936 4 Sheets-Sheet 3 INVENTOR.

Feb. 13, 1940. J. NEUFELD 2,190,037

I STABILIZING METHOD AND DEVICE Filed Nov. 25, 1936 4 Sheets-Sheet 4 AMPLIFIER INVENTOR Patented Feb. 13, 1940 2,190,037 k s'ranmzme vmrnon AND DEVICE Jacob Neuield, Tulsa, Okla. Application November 25, 1936, Serial No. 112,743

4 Claims.

This invention relates to a method'and means for maintaining stable patterns of antenna systems.

In the recent times' considerable attention has been given to the problem of maintaining a stable pattern in directive antennas both in the broadcast field and inthe radio range beacon transmission.

In the broadcastfield antenna arrays which would transmit all their power in one or more directions and will present no radiation in another direction can be utilized to eliminate interference between adjacent transmitting stations 'and would increase thenumber of stations which would operate on a single channel. This necessitates the maintenance of correct phase and amplitude relations between the currents in the various antennas'of the array. Such relationships are subject to many perturbing effects and a great dimculty has been experienced in the prior art in maintaining the directivity of antennas within allowable tolerance.

In the radio range beacon transmission where the safety of an aircraft is involved the require ments for maintaining a stable antenna pattern are much more rigorous than in the broadcast field, and I shall therefore illustrate my invention as applied to the beacon antennas. It is however well understood that my invention is equally applied to broadcast antennas and 'to any other antennas and I desire to claim all novelty inherent in the invention as broadly as the prior art permits.

In systems commonly employed for aligning airways the on course zones are determined by the intersection of two space patterns from two independent antenna groups. Any change in one antenna group will change the intersection and shift the course indication. Consequently, it is necessary that the phase relations between the currents be maintained to a considerable accuracy in order to assure the stability of the two space patterns. Considerable" difiiculty, has been experienced, however, in the past maintaining. this accuracy within the allowable limits; It has been recognized that a minute change of tuning in one of the antennas for any reason, such as the efiect of nearby poles, faulty insulators, etc. during wet weather, will result in a change in phase may impair considerably the safety of an aircraft.

' It has also been found some time ago that freangle between the antenna currents. Thisoauses unintentional shifting of the airway courses and quently considerable shifts in course took place which have been caused by conditions other than those resulting from the detuning of an an-v tenna. In such cases the plane of polarization of horizontal field components which was due to the horizontal parts in the. loop antenna was shifted during the night on account of reflection from ionized layers in the atmosphere.

It is therefore an object of my invention to eliminate all the inconveniences of the prior art and to provide a radio range beacon transmission system in which all unintentional shifting in the direction of the aligned courses will be eliminated.

It is a further purpose of my invention to provide a stable radiation pattern for anantenna it system free from various perturbing influences. I It is a further purpose of my invention to maintain automatically predetermined phase relationships between various currentsof an electrical system. i

h It is a further purpose of my invention to maintain automatically predetermined phase and current relationships of an electrical system.

, his a further purpose of my invention to provide a means sensitive to a phase change between two currents and to the direction in which this phase change occurs. A

Further purposes appear in the specification and in the claims.

My invention involves both the method and th subjects matter. In accordance with my invention I provide an arrangement for stabilizing the radiation pattern of an antenna system in which I include two receiving antennas placed in the radiation field at two assigned locations in which the intensities of produced signals bear 'a certain predetermined relationship one to another. The antennas are mutually connected in a manner as to oppose the efiects resulting from the received signal and to produce a combined efiect which is zero as long as the radiation pattern is maintained stable. If, however, the radiation pattern changes, the eflect derived from one antenna increases while the effect derived from another antenna decreases thus causing the appearance of the combined effect the magnitude and the direction of which represent the change of the radiation pattern. The combined'eflect is made to act upon one of the parameters of the antenna system in a manner as to counteract the cause which has produced the unintentional change-in the radiation pattern and thus to maintain the stability or the pattern. A better understanding of the invention may be had by referring to the following detailed de- "scription which is, accompanied by drawings in which; Y 1

Fig. 1 shows a normal space pattem for 'four beacon courses 90v degrees apart.

Fig. 2 shows the space patterns of a pair of antennas in which currents differ in time phase by various amounts.

v Fig. 3 shows an arrangement 'for stabilizing the radiation pattern of a pair of antennas.

Fig. 4 shows a modified arrangement for stabilizing the radiation pattern 'ofapair of' antennas.

Fig. 5 shows the superposition of two normal figure-in-8 patterns of unequal intensity for four beacon courses in which two sets at 180 degrees are at an angle differentfrom 90 degrees.

' Fig. 6 shows schematically the general arrangement of a radio-range beacon transmitting station.

' Referring now more particularly to Fig. 1, the

numerals l0 and H represent the usual figure- 'o f.-8 transmission characteristic'for giving the visual or aural type radio beacon courses l2, l3, The arrangement for producing these courses may preferably take ,place by means of the transmission line type of antenna system described in the Bureau of Standards Journal of Research. vol. '10, Jan. 1933, Research Paper 30 #513 entitled: The cause and elimination of night efiect in 'radio rangebeacon reception by Harry Diamond-see particularly under subtitle V Transmission-Line Antenna System (pp. 23-- 33.of the said research paper).

The use of the transmission line antenna systhe time phase angle between thev currents in the antennas of 'each pair. When the time phase angle is 180 degrees, a true figure-of-8 space pat- 40 antennas, a cardioid is obtained. For phase angles intermediateto those two values, a space pattern intermediate to the true figure-0H! and cardioid results. Fig. 2 illustrates the dependence between the phase displacement of currentsin two opposite antennas of a pair and the resulting space pattern. In this figure, Ill represents the space pattern corresponding to the diiierence in phase of 180 degrees between the currents of antennas l1 and I9 respectively; l0-m corresponds to the case in which the current in the antenna I9 leads the current in the antenna [1 by 165.degrees'; and Iiil; represents the space pattern when the current in the antenna l9 leads the current in the antenna I! by 150 degrees.

The control of the phase relationships in a pair of antennasprovides a method. for altering the radiated space pattern to permit alignment ferring to Fig.1, it the phase angle between the currents in one pair of antenna be changed from 180' degrees to 165 degrees, the correspondingspace pattern changes so that the polar diagram at its intensity is not any more Ill. but its (see 2). Superposition of the pattern we (instead or II) and 0! thepattern liwill give tour equisignal zones diilerent from those designated by l2, l3, l4, lt-in Fig. 1.

The use of the above method or altering-the angular direction oi. the beacon courses in order to align them with airway :r'outes'is clearly shown in Fig. 16, p. 30 m the referred-research paper by HarryDiamond.

" u The property of this antenna system which Fig.- 7' shows another means for stabilizing the g0 radiation pattern of an antenna system.

tem involves the problem of accurate control of term is obtained. When '11; is 180 degrees the space phase angle between the two vertical 0! the beacon courses at arbitrary angles. Re-

aicacsv antennas of a pair. Obviously the phase angle between the currents in the two vertical an- 8 tennas of a pair must be kept constant within rather close limits, or the angularv direction of the beacon courses will vary from timeto time. It has not been possible in many instances to maintain this constancy of phase within certain 10 preassigned tolerances. Very frequent and unintentional changes in the phase relationships were observed and which were due to various accidental causes of random nature and beyond human control and resulted usually from the 15 effects of nearby poles faulty insulators during wet weather, etc. Since the safety of an aircraft depends upon a stable pattern such phase changes cannot be tolerated and it is necessary that the phase relations between the currents be maintained at a very great accuracy. m In accordance with my invention I am slfow wing in Fig. 3 one of the embodiments of my in- ;vention illustrating a means for maintaining'an antenna pattern stable and which has been chosen with a view to simplicity of operation and convenient illustration of the principles involved. Referring now more particularly to Fig. 3 the schematic diagram illustrated thereinrepresents one half of a complete antenna system required for a range-beacon installation. Numeral represents a transmitter which is connected through the transformer. 3i totwo-wire parallelconductor transmission lines 32 and 33 respectively, the-transmission lines being of such a w nature as not to radiate. The transmission line 32 is .used to feed power from the transmitter 30 to the antenna I! by means of. a radio frequency transformer while the transmission line 33 feeds powerirom the transmitter 30 to the antenna 19 by means of a radioirequency transformer 35. The antenna l! provided with a loading coil 36 (to resonate it at the frequency ,of the transmitter) and a fine tuning coil 37 for more minute adjustments. In a similar manner t e antenna I9 is provided with a loading coil and a fine tuning coil 39. Assume now that the current flowing in the antenna l9 leads the current in the antenna I! by 165 degrees. Consequently the resulting radiation pattern 'will'have the form represented by numeral 10a in Fig. 2. In this radiation pattern the points M and N (shown in Fig. 2) c rrespond to certain locations; at which the'stre h of the respective signals has a predetermined ratio. Let for in- 55 stance the signal strength at M be a/b times larger than the signal strength at N. At the referred pointslvl and N are placed :receiving antennas which are shown in Fig. 3 and designated respectively by numerals 40 and 4|. The 60 receiving antenna 4| is provided with an inductor 42 while the receiving antenna 4!) is provided with an inductor 43.

Referring again to Fig. 3, the numeral 44 designates a three electrode tube provided with an "5 anode 45, cathode 46 anda grid 41. The anode 45 is connected to one end of the tuning coil 39 of the antenna 19 by means of an arrangement including an inductance 49 in series with a by pa capacitor 50 (of substantially zero reactance). m The cathode 48 is connected to another end of the tuning coil 38 and to ground through a biasing battery 48. 'Ihe grid is connected to ground by means of a path which consists of resistors II and I2 in series and shunted by the u ence between the currents in the antennas I1 and capacitors 53 and 54. Rectifiers and 58 are provided which contain cathodes 51, 5B, and two anodes 59, respectively. The anodes 53, 30 have a common terminal 6| with the resistors 5i and 52. The cathode 51 is connected to the resistor 5| by means of a path including the resistor 62 and the secondary winding of the transformer 63. The cathode 58 is connected to the resistor 52 by means of a path including the resistor 64 and the secondary winding of the transformer 65. The primary windings of the transformers G3 and are included in the circuits 66 and B'l'respectively. The circuit 66 is inductively coupled to the receiving antenna 4|) by means of a winding inductively coupled to the receiving antenna 4| by means of a winding 69.

The operation and performance of this arrangement can be explained as follows:

In order to eliminate the radiation from the transmission lines 32 and 33 the input impedances of the radio frequency, transformers 3% V and 35 must be respectively equal to the surge impedances of the lines. If the terminating impedance is not equal to the corresponding line impedance, part of the wave reaching the terminating impedance will be absorbed by it and part of the wave will be reflected along the line.

- This in part sets up standing waves and causes radiation from the line. transformers 34 and 35 employed for coupling The radio frequency the transmission lines 32 and 33 to the vertical antennas l1. and iii are accordingly designed so that the input impedance of each is equal to the surge impedance of the respective transmission line. In this way radiation from transmission line is eliminated. The proper adjustments necessary in order to insure the equality between the surge impedance of .the line and the input impedance are described in the referred research paper by I-Iarry Diamond, chapter V, pages 32-33.

The variable inductors 31 and 39- shown in series with the vertical atennas l1 and I9 serve for minute tuning of the antenna to the radio frequency of the transmitting set. It has been recognized, however, that due to various per-- turbing effects, an antenna l9 (or H) when tuned to the frequency of oscillation does'not remain tuned after it has been once adjusted by the variable inductance/39, but drifts away from the tuning conditions to which it has been set.

A slight change in tuning of one antenna will cause a decided shift of phase between the currents of two opposite antennas and consequent shifting of the course. If it is arbitrarily said that the maximum allowable shift of course shall be :2 degrees, then the phase of the currents must be. correct to within :2 degrees. A shift of such magnitude, can occur with a very slight change in antenna constants. To consider a specific case (see F. G. Kear: Phase Synchronization in Directive Antenna Arrays with Particular Application to the Radio Range Beacon, Bureau of Standards Research Paper RP581, p. 126) assume a vertical tower feet high with a resistance-of 10 ohms and a capacitance of 500 mrnf. The phase angle between the current and voltage is zero when the antenna is exactly in tune. For an angle of '2 degrees a change in capacity of 1.2 mmf. is all that is necessary. Such a change could readily be caused by the effect of rain or snow. It is-apparent, therefore,

, that some means of phase control must be pro- 68 and the circuit 61 is ductor 42 of the antenna 4|.

l9 it is necessary to introduce an effect which will tend to overcome any change in tuning-condition and which will be controlled by the 'departure from the said tuning conditions. The controlling element which will counteract the detuning will be in this particular case the vacuum tube 46 which is included in a circuit across the inductance 39. The plate circuit of the vacuum tube 44 acts as a resistance and the magnitude of this resistance is controlled by the grid voltage. As can be seen a variation in plate resistance of the vacuum tube 44 will cause a change in tuning of the antenna 19. This is due to the fact that the equivalent inductive component of the circuit including the inductance 39, the inductance 49 and the tube plate resistance of the tube M will change with a variation in the magnitude of the plate resistance of the tube 44. It is thus seen that a variation in the grid bias of the tube 44 will modify the'tuning conditions of the antenna l3 the radiation pattern of the antennas I1 and I9 is stable and the intensity of the radiation field is shown schematically on the polar diagram Illa of Fig. 2. Then the intensity of the field in point M is a/b larger than in the point N and consequently the voltage induced across the inductor 43 of the antenna 30 is a /b times larger than the corresponding voltage acrossthe in- The voltage across the inductor 53 is transmitted by means of the circuit 63 to the secondary winding of the transformer 53. This voltage causes a unidirectional current to pass through the path which includes the plate 59, cathode '61, resistor 62, primary winding of the transformer 63 and resistor 5L.

The steady part of this current passes through. the resistor 5! in the direction indicated by the arrow and causes a drop of potential between the terminals of this resistor. Similarly, the alternating voltage across the inductor 42 of'the antenna M is transmitted by means of the circuit 61 to the secondary winding of the transformer 65. This voltage causes a unidirectional current to pass through the path including the plate 60,

cathode 58, resistor 84, primary winding of the transformer 35 and resistor 52. The steady Partof the current flowing through this circuit passes through the resistor 52 in the direction indicated by the arrow and causes a drop of potential between the ground and the terminal 6|.

Consider the case when the phase difference between the antennas i1 and i9 is maintained exactly at predetermined value of degrees and consequently the voltage developed across the inductor 43 is a/b times larger than the voltage across the inductor 42. The resistors 5| and 52 have been, however, so proportioned that the voltage drop in'one-of them equals the voltage drop in another. Now since these voltages are opposite in sign and in series the resulting voltage which is equal to their I sum and is applied between the ground terminal and the grid 61 of the tube 44 is zero. Thus the effect upon the grid quently the phase difi'erence between the current voltage of the tube 4 is equally zero and the tuning condition of the antenna it remains unaltered. v

Now suppose that due to an external influence such as mentionedv above, the inductance of the antenna i9 slightly increases. Consequently a certain lag of 0: degrees appears between the current in the antenna I9 and the voltage in the antenna I9. Under normal conditions the currentsin the antenna l9 leads the current in the antenna I! by 165 degrees. At present, however, due to the detuning the phase angle becomes 165-11 degrees and this changes the space pat-- tern in such a manner that the intensity of field at point M (see Fig. 2) becomes stronger while the intensity of field at point N becomes weaker. This causes an increase of voltage across the inductor 43 and a decrease of voltage across the inductor 42. I

Now the voltage across the inductor 43 is larger than a/b times the voltage across the inductor 42. Consequently the voltage across the resistor M will be larger than the voltage across the resistor 52. Since the resistors 51 and 52 are in series and the referred to voltage drops are in opposite directions the resultant voltage between the earth terminal and the point 10 will be equal to the difference between the absolute value of the voltage drop across the resistor 5| and the voltage drop across the resistor 52 and the polarity will be such that the point Ill will become positive with respect to the ground terminal. Now since the point I0 is connected to the grid 47? of the tube 44, the potential of the grid of the tube 44 becomes more positive. This has an effect such as to reduce the negative grid bias between the grid and cathode of the tube 44 (this negative grid bias being supplied by the battery 48). The tube 44 is operating in a circuit the constants of which are such that the operation is over a curved portion of its grid voltage-plate current characteristic (the lower knee of the curve) in such a manner that increasing the grid potential positively decreases the A. C. plate cathode resistance of the tube 44. As it is shown in the figure this A. C. resistance forms a shuntoi the inductor 38 and influences the tuning conditions. of the antenna IS in such a manner that if the A38. resistance of the tube decreases the inductive reactance of the antenna also'decreases. Consequently, any tendency to cause the increase of the inductance in the antenna IB' is immediately counteracted. It can be shown similarly that any tendency to decrease the inductance 'l9 is correspondingly counteracted by'the reverse-action of the same auxiliary circuit. This means that the auxiliary circuit represented by the numerals ill to 10 inclusive has an efiect on theantenna arrangement which is stabilizing as to the phase variations. That is, any tendency to cause the drift in phase or the current in the antenna I! the lagging direction is immediately counteracted v with respect. to the current in the antenna i! in by the action oi the said auxiliary circuit.

It can be shown similarly that any tendency 1 to cause the drift of the current in the antenna ill with respect to the current oi the antenna Win.

in the antenna I! and the current in the antenna 69 is maintained constant.

It is apparent that the effectiveness oi" the control of the associated circuits depends'upon the circuit constants, the amplification factor of the tube 45, the rectification efficiency of the tubes as and 56, etc and approaches as alimit the ideal condition. Its action is such that it only reduces the amount of drift, but usually does not reduce it to zero. It is apparent to those skilled in the art. that the degree of effectiveness of the circuit is controlledby the circuit constants and can beincreased at will to approach as nearly as desired to the ideal limit of zero drift. Itjs well from another without rectification can be efiected by means of a dynamometer type electric meter. In this arrangement the voltages across the two receiving antennas are added in series opposing and then impressed across one of the.

coils of a dynamometer type meter, the other coil of the meter having impressed across it part of the voltage being carried by the main osciilator. The motlonof the needle of the dynamometer will then be a measure of the amount of detuning both in magnitude and in direction. Now, as it has been described previously, after an electrical effect has been produced which is a measure of'the detuning the said effect can be made to act upon one of the antennas in a mannerso as to stabilize its tuning and to counteract any drifting. One method of acting upon the tuning of the antenna has been in the description of Fig, 3 the said method was entirely electrical in nature. It is, however, possible and sometimes convenient to act upon the antenna mechanically in a manner so as to change its tuni'ng conditions. This variation of its tuning conditions is accomplished by the changing of the value of one of the reactive parameters of the antenna tuned circuit. This can be accomplished by means of some electromechanical device such. as small mo= tor or solenoid or electromagnet which will act mechanically upon the capacitance or inductance of the antenna in response to the electric currents or voltages which measure the amount of drift in the tuning For example, a small variometer, or other variable inductance or a small condenser with one movable plate. The mechanical displacement and consequently the electrical magnitude or this variable reactance can be controlled by the electrical voltage or current which is a measure of the amount of drift in tuning the antenna and can be made to vary the said reactance so as to counteract or tend to counteract the said drift. The mechanical displacement of the variometer coil or the condenser plate can be conveniently combined with means for indicating visually the exactness of tuning. The dis-V placement of the variable inductance or variable capacitance can be controlled either by the difierence in the. rectified voltages of thlux:

iliary circuits described in connection with Fig.

3 or could be controlled directly by the difference of the two voltages by means 01 the suitablyarranged dynamometer" type meter described above. The circuit shown in Fig. 4 illustrates diagrammatically in greater detail the system in tatable winding 82.

which a mechanically movable arm is made to control, the tuning of .the antenna.

The elements which are common to Fig. 4 and to Fig. 3 have been denoted by the same numerals; their performance has been described above and need not to be explained here. Briefly, numeral indicates the transmitter, 82, 83, transmission lines feeding the currentinto the antennas'il and I8. Numerals 88 and 88 represent the loading coils of antennas I1 and I9 respectively. The antenna I8 is provided also with a tuning coil 88 having a form of a variometer and including a stationary winding BI and a ro- The rotatable winding 82 is mounted on an arm 88, the said arm being .capable. of rotating about point 88 representing an axis perpendicular to the drawing. Fastened to the arm 83 is' a coil 88 which constitutes the 7 moving coil of the dynamometer arrangement 88. The fixed coil of the dynamometer arrangement designated by 81 receives the current from the transmitter 38. The moving coil 881s connected across the output terminals of the amplifier 88. The input circuit of the amplifier 88 is coupled .through the transformer 88 to a .circuit 9i. The circuit 9I includes resistors 83, 88 and windings 88, 88. The windings 88, 89 are respectively coupled to the receiving antennas 48 and 8|. The operation of the circuit is as follows: Suppose that the phase difierence between the currents in the antennas I1 and I9 is correctly ad- Justed in order to give the desired space pattern. Under these conditions the voltage induced by the antenna 88 in the circuit 9i through the wind- -'ing as is equal to the voltage induced by the antenna M in the circuit 8| through the winding These induced voltages are inopposition, and consequently their eiiects are mutually cancelled and there is no current flowing in the circuit 8 I Under these conditions there is obviously no current which would be forwarded to the 1 amplifier 88 from the circuit 8| and which would be subsequently transmitted to the coil 85. Consequently the current through the coil 85 will be zero. The coil 87, however, is energized directly from the transmitter 88 and the current through .it is determined by the current limiting resistor 98. Since however the current through the coil 85 is substantially zero, there will be practically no magnetic interaction between the two coils and the coil 88 will remain in its position of rest. .Now suppose that because oi the various exterior causes which have been previously described the antenna I8 becomes detuned by a slight increase of its reactance. Consequently, a certain lag of 1: degrees' appears between thecurrent in theantowns and the voltage in the antenna I8. Under normal conditions the current in the antenna I8 leads the current in the antenna IT by 165 degrees. At present, however, due to the detu'ning the phase angle becomes 165 degrees and this changes the space pattern in such a manner that .theintensity of field at point M (see Fig, 2) becomes stronger while the intensity of, field at point N becomes weaker. This causes an increase of voltage across the inductor 48 and a decrease of voltage across the inductor 42. This will resuit in the increase of voltage induced in the cir- 3 cuit 8! by the antenna 88 and in the decrease or voltage induced in the circuit SI by the antenna BI. These two voltages are impressed in the N circuit 9| in the opposite directions and cause a current to flow. This current is amplified in the amplifler 88 and applied to the movable dynamometer coil 85. Now the winding directions of coils and 81 are such that due to their magnetic interaction there is a force acting. This force causes a rotational movement of the arm 88 to which the coil 85 is-fastened. Consequently, the inductance of the variometer 88 is varied in such a manner as to oppose the slight increase'in the antenna inductance which was the cause of the detuning. Nowin the case-when the inductance of the antenna I8 decreases the action of this arrangement is very similar in the fact that the balance of the voltages induced in 8| by the antennas 88 and M is disturbed. However, in the case of decrease of inductance it is the voltage induced by the antenna 82 that is increased and the voltage induced by the antenna 40 that is decreased. So that the voltage impressed upon the amplifier 88 is of opposite phase oi. the voltage which would be caused by the increase of inductance in the antenna I9. Consequently, the current flowing through the movable coil 85 of the dynamometer mechanism 86 l is of an opposite phase, to that in thepreviously described case. The operation is otherwise analogous but in opposite sign as the magnetic interaction between the coils 88 and 81 is, such that the coil 85 tends to move away from its position of rest in a direction opposite to that which it had previ I ously.

It is evident therefore that the stabilizing influence of the circuit arrangement is equally efflcient in the case of the phase drift in the lagging or in the leading direction between the currents in the antennas I1 and I8. The action of the arrangement being such that at any instant ii an influence acts upon the antenna so as to change the phase of the current flowing through this antenna in relation to the current flowing in another antenna then immediately the circuit acts in a manner so as to counteract and neutralize the said drift.

It is therefore obvious that I have provided a means for maintaining a course all M'- independent of various accidental and unintentional effects.

In general, various conditions for course aiignangles of the normal figure-in-8 pattern as designated by II in Fig. 1 with a distorted pattern as designated by Na in Fig. 2. Still another condition may be secured in which the two sets of 180 degrees are at an angle different from 90 degrees.

This condition'is illustrated in Fig. 5 in which the four beacon courses I 82, I I8, H8, I It, are formed by a superposition of two normal figure-in-8 patterns H8 and III of unequal intensity, the pattern I I8 being more intense than the pattern I I I.

The general arrangement ior producing a pattern as shown in Fig. 5 for a double modulation radio-range beacon is shown in Fig. 6. .Reierring now more particularly to Fig. 6 the dotted block denoted by the numeral I28 designates a transmitting set which is coupled into the transmission lines I2I, I22, I28, I28, through a goniometer included in the dotted rectangle I25 and coupling coils I28 and I2-I. The transmission lines are in turn coupled through thetransformers I28, "avg block-I4I and transmits the modulated carrier to the power amplifier I42.

In the previous embodiments shown in Fig. 3-

and 'Fig.. 4 means were provided for maintaining the space distribution of a pair of antennasin such a manner that the phase displacement-bestant.

'digg s pectively and which are transmitted to the said tween the currents in these antennas was automatically kept at 165 degrees-and consequently the polar'diagram l0 a (see Fig. 2) was maintained invariant. It is well understood, however, by those skilled in the art that. when the patterns of two pairs of "antennas are superposed theiinvari'ancy of each of the said patterns. In

many cases various accidental and unintentional changes occur in the relative strengths of the two superposed patterns and this causes shifts in the direction of courses and impairsconsiderably to the conditions of safety of an aircraft.

In this embodiment I am therefore providing means of maintaining constant the direction'of the aligned courses resulting from the superposition of two patterns by maintaining the form of each of the patterns invariant and also by maintaining their relative strengths constant.

Consider again the space pattern shown in Fig. 5. In order to eliminate any accidental and unintentional shifting of the courses H2, H3, H4, I I5, a provision should be made for the-following:

1. The space pattern radiated by the pair of antennas I33 and I35 (Fig. 6) must maintain stable its normal figi1re-in-8 pattern.

2. The space pattern radiated bpthe pair of antennas I30 and I32 (Fig. 6) must maintain stable its normal figure-in-8 pattern.

3. The relative strength of the pattern I III with regard to the pattern II I (Fig; 5) must be con- In order to satisfy the conditions (1) and (2) means are employed which are similar to those explained above in connection with Fig. 3 or Fig. 4. For instance, the pattern radiated by the antennas I33 and I35 is maintained stable by means of two receiving antennas placed at points A- and B respectively. The points A and B are preferably located in. thevertical plane which passes through the antennas I33. and I35 and intersects the plane of the figure along the line V. Under normal. conditions the voltage induced in the receiving antenna placed at point A bears a certain predetermined relationship tothe voltageinduced in the receiving antenna placed at I point B. These two voltages are transmitted to an auxiliary circuit arrangement which is substantially similar to theone designated by the numerals 5I to 10 inclusivein Fig. 3 and operates in the manner explained above. Briefly, if the phase relationship between the currents inthe transmitting antennas I33 and I 35 are correctly adjusted the voltages which appear at the receiving antennas located at points A and B rea uxiiiary arrangement oppose their eflfects and produce a combinedefiect which is zero as longas the parameters of the antennas I33 and I35 maintain their values constant. If ,-however, due to weather conditions, wind, temperature, etc,

'the parameter of one of the antennas,'for in-. w 'stance of the antenna I35 changes slightly its value, the" pattern radiated by this antenna becomes distorted. Then the voltage transmitted bythe receiving'antenna at A to the auxiliary circuit changes its relative value with regardto the voltage transmitted by "the receiving antenna at B to the said auxiliary circuit and thecombined effect is no longer zero; its magnitude and direction represent the change of the radiation pattern. This combined effect is made to act upon the parameter of the antenna I35 in a manner as to counteract the cause which has produced the unintentional change inthe radiation pattern. p

In a similar way any unintentional variation of a parameter in the antennas I32 and I34 may be counterbalanced by an efiect which is derived from two receiving antennas placed at point-s0 and D respectively. The points C and Dare located preferably on the axis in vthecvertical plane which passes through antennas I32, I34, and intersects the plane of the figure along the linewfi The receiving antennas placed 'at'points C and D act in the same manner asthe. antennas placed at points A and B upon an auxiliary'arrangement which is similar to the arrangement which is designated by the numerals 5I-I0 in- Fig. 3. If the phase relationship between currents in the antennas I32 and I34 slightly changes its value due to the driftof one of the parameters the said auxiliary arrangement is made to act on a pa.- rameter in one of the antennas I32, I34, in such a manner as to counteract the said change in the value of the parameter and to maintain the cor-. responding space pattern in its normal, figurein-B form. f T

In order to satisfy the condition (3) consisting in maintaining the relative strength of the pattern IIII with regard to the pattern III constant an auxiliary arrangement is provided which containsineans similar tothose represented by the numerals 5I- -I0 in Fig. 3. This arrangement is shown in Fig. 7 which should be examined in represent 'two receiving antennas which have been appropriately placed at the points E and F respectively (see Fig. 5) in the space pattern ofthe antennas I32, I33, I34, I35. In the Fig. '7 the rectangular block 202 includes an auxiliary arrangement which is similar to the one designated by the numerals 5I-85 inclusive in Fig. 3. In this auidliary arrangement the elements which correspond to those of Fig. 3 have been designated by the same. numerals with the difference that to the numerals designating the elements of Fig. 7 the subscript a has been added. Thus a resistor 5Ia in Fig. 7 corresponds to the resistor M in Fig. 3, the rectifier tube 550: in Fig. 7 corresponds to the rectifier tube 55 in Fig. 3, etc.

The rectangular block 203 includes the radio frequency amplifier in which the modulation is produced and which has been designated by the numeral I3! in Fig. 6. Numeral 204 designates a fragment of a power amplifier which has been designated by the block no in Fig. 6. Block I39 amplifier is connected to the power amplifier204 by means of a coupling'205. The coupling 206 suitable for the so-called plate modulation. It.

includes a tube 208 provided with cathode 209 grid 210 and anode 2. The numeral 2l2 designates a self-biasing arrangement in the grid circuit of the tube 208. The plate circuit of the tube 208 includes an oscillatory circuit 2I3, a

secondary winding of the transformer 210, a resistor 2l5 in series with a b'attery'2l0. The resistor M5 and battery 2i6 are shunted by a tube 2". The tube 2ll includes a cathode 2l8, a grid '2l0, and anode 220. The grid voltage of the tube 2|! is the sum of the voltage delivered by the battery HI and the 'voltage resulting from the potential drop across the resistors 52a. and SM.

The operation of this arrangement can be explained as follows:

Under normal conditions the relative strength of the pattern H0 is maintained at a predetermined value with regard to the strength of the pattern HI. Consequently the voltage transmitted by the antenna 200 to the block 202 bears a predetermined ratio to the voltage transmitted by the antenna 20| to the block 202. These two voltages are subsequently applied through the transformers 63a and 65a to the rectifier 55a and 50a respectively. Consequently, a rectified voltage appears across the resistor ila audit is equal and is of opposite sign to the rectified voltage which appears across the resistor 52a. Thus the voltage between the ground terminal and the grid N9 of the tube 2H is zero. If, however, the relative strength of the pattern H0 changes with regard 'to the strength of the pattern HI (see Fig. 5) the voltage derived from the antenna 200 changes its magnitude with regard to the voltage derived from the antenna 20! Then the rectified voltage across the resistor 51a is not equal to the rectified voltage across the resistor 52a. Consequently the resultant voltage between the earth terminal and the grid 2l0 is not equal to zero. Its magnitude and direction represents the departure from the relative strength of the pattern H0 with regard to the pattern I l I. So that any variation of the relative strength of the pattern H0 with regard to the pattern ill is immediately counteracted by the 'efi'ect introduced by the auxiliary-arrangement 202. This has an effect such as to change the grid voltage of the tube 2". It is known to those skilled in the art that the change of the grid potential of the tube 2|! changes the A; C. plate resistance. Since the tube 2H is inserted across the resistor-2 I5 and the battery 2! in the plate circuit of the tube 208, it follows that the change of the grid potential of the tube 2" changes the plate resistance of the tube 208. Consequently any tendency to change the relative strengths of the pattern H0 and ill causes a change to the plate voltage of the tube 208 andconsequently changes the power output of the modulated amplifier 208. I

The radio frequency oscillations are transmitted from the master oscillator (shown in Fig.

'6) through the coupling 200 to the grid 2! of the amplifier tube 208 and they appear in the amplified form in the plate circuit of the tube 200. The modulator I39 is coupled to the plate cally their current and circuit of the amplifier by means of the transformer 2M. Thus the audio frequency voltage transmitted from the modulator to the plate circuit of the amplifier is superposed on the D. C. voltage of the battery 2|6. Consequently the radio frequency oscillations in the plate circuit of the tube 208 are modulated by the audiovolttions are in turn transmitted through the coupling 205 to the power amplifier 200. As it is well known by those skilled in the art, the power delivered by the modulated amplifier depends upon explained above that by varying the effective plate cathode resistanceof the tube 2 H the plate resistance of the tube 2i3 is varied.

ages induced into the plate circuit through the transformer 2M. The modulated R. F. oscillathe resistance in its plate circuit. It has been i H Now, it can be readily understood by those skilled in the art that any variation in the strength of the pattern H0 with regard to the pattern III is immediately counteracted by the effect introduced by the auxiliary arrangement.

202 (Fig. 7). This counteraction is caused by the following sequence of events: Any slight change in the relative strengths of the patterns H0 and HI causes alchange in the grid voltage of the tube 2|! and this in turn causes a variation of the plate resistance of the tube 208 and consequently changes the power output of the amplifier 208. The change in the power output of the amplifier 200 is done in such a manner as to oppose the variation in the relative strengths of the patterns H0 and III in order to maintain the direction of, the courses invariant.

It is therefore apparent that I have provided a method and means for stabilizing directive properties of antennas by maintaining automatiphase relationships .constant.

In view of my-invention and disclosure variation and modifications to meet individual whim or particular need will doubtlessbecome evident to those skilled in the art, to obtain part or all of the benefit of my invention without copying the structure shown, and I therefore claim all such in so far as they fall within the reasonable tionships for producing a pattern of desired space characteristics, means in the said pattern responsive to a change in the said space characteristics and associated with the said aerial layout for maintaining the intensities of currents at a predetermined relationshipand another means re sponsive to a change in the said space characteristics and associated with-the said aerial layout for maintaining the phases of currents at predetermined relationships.

2. In a radio beacon the combination with a source of radio frequency currents of amplifiers for amplifying said currents, modulation devices for modulating'currents in each of said amplifiers by a, different signal, a goniometer compris-v ing fixed stator windings and rotor windings crossed at predetermined angles and rotatable about a common axis with respect to said statorwindings, the said goniometer. receiving the outputs of the said amplifiers, transmitting antennas eter which controls individually its radiation for modula placed in the radiation patterns oi'the transmitting antennas and coupled with the controlling circuit, the said controlling circuit being differentially responsive to the outputs of the said rev ceiving antennas and controlling the parameters of the'transmitting antennas in order to maintain' the radiation pattern of the radio beacon stable.

' 3. In a radio beacon the combination with a source of radio frequency currents, of amplifiers for amp g said currents, modulation devices g currents in each of said amplifiersby a different signal, a goniometer comprising fixed stator windings and rotor windings crossed at predetermined angles and rotatable about a common axis with respect to said stator windings, the said goniometer receiving the out- .puts of the said amplifiers, transmitting antennas tuned to the radio frequency of the said source and connected to the said goniometer,

a controlling circuit, receiving antennas placedin the radiation patterns of the transmitting an-" tennas and coupled to the said controlling cira oopa'r cuit, the said controlling circuit being difierentially responsive to the output of the said receiving antennas, an electronic tube in the plate circuit of one of the said ampliflers,- and means for controlling the electronic tube by the said controlling circuit in a direction to continually maintain the same relative magnitudes of the power outputs in the said amplifiers.

4.- In a method of aligning beacon courses with a plurality-01' airways by superposing a plurality of space patterns of a plurality of antenna systaining the directions of the said courses invariant.

JACOB NEUF'EELD. 

